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#166 Problems in Punching and their Countermeasures (5) Trimming of Drawn and Shaped Parts

Category : Die Design
July19, 2013

In drawing or shaping, it is common to prepare the shape while shrinking the outer periphery of the blank. Because of this, the flange edge part after forming will have changed from the shape of the original flange edge part and has an irregular shape. For example, if a cylinder is drawn from a circular blank, very often we see that the flange shape after drawing is not a neat circular shape but is a shape closer to a rectangle. The shape of the edge will be far from the edge shape required in the product and hence trimming will be necessary.

Fig. 1 explains trimming of drawn products. As shown in this figure, the scrap obtained after trimming has the shape of a ring. In this condition, the scrap gets stuck to the punch of the die and cannot be taken out of the die. In order to remove the scrap, it is necessary to divide the scrap into two portions. In the case of small products, the scrap is usually removed by dividing it into two parts. Fig. 1

If the operation is a single step operation (one shot operation), if the scrap is separated from the die, the processing thereafter is not particularly a problem although it is somewhat cumbersome. However, if the shape of the product becomes large or if trimming is to be done in an intermediate process in transfer forming, it is necessary that the removing of the scrap needs to be done without any problems.

If the product becomes large, the scrap will be too large and even if removed from the die by dividing it into two parts, very often the processing thereafter (recovering by sliding above the chute, etc.,) cannot be done well. It is good that the scrap is made into appropriate sizes that make their processing easy. Fig. 2 shows such an example. The size of the scrap is made small using two steps thereby making the processing easy.

Fig. 2

In shaping operations, attention is given strongly (of course, naturally) to the formed shape, and problems can occur if trimming and scrap processing is taken lightly. Care should be taken about these.

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